Astore sells small notebooks for $7 and large notebooks for $10. if a student buys 6 notebooks and spends $51, how many of each size did he buy?

3 small notebooks and 3 large notebooks

Step-by-step explanation:

The cost spent by the student is the sum of the cost spent on small notebooks and the cost spent on large notebooks.

The cost spent on small note books is the product of the cost per notebook and the number of small note books purchased.

let the number of small and large notebooks purchased be a and b respectively,

a + b = 6

and

7a + 10b = 51

since a + b = 6,

b = 6 - a

7a + 10 (6 - a) = 51

7a + 60 - 10a = 51

-3a = 51 - 60

-3a = -9

a = 3

since b = 6 - a,

b = 6 - 3

= 3

Hence he bought 3 small notebooks and 3 large notebooks.